Remote signal generators capable of sending command signals are known. FIG. 1 shows an electric lamp wall box dimmer 12 coupled to a remote signal generator 10 through two conductors 14 and 16. A wallbox dimmer and remote signal generator are available from the assignee of the present application and known as the Maestro dimmer and accessory dimmer. The wall box dimmer comprises a signal detector 32 capable of receiving and decoding three discrete signals generated by the signal generator 10. The signals are generated when a user actuates momentary contact switches "T", "R" or "L". The "R" switch generates the signal shown in FIG. 2A when actuated which causes the dimmer to increase the light intensity of the coupled load 20. The "L" switch generates the signal shown in FIG. 2B when actuated which causes the dimmer to decrease the light intensity of the coupled load 20. The "T" switch generates the signal shown in FIG. 2C when actuated which causes the wall box dimmer 12 to turn on to a preset light intensity, go to full light intensity, fade off slowly or fade off quickly. Each time the switch "T" is actuated, the signal generated and sent to the signal decoder 32 is always the same. To cause the dimmer to react differently to the closure of switch "T", the user must actuate the "T" switch differently. When a user actuates switches "R", "L" or "T" the signal detector 32 actually receives a string of signals because the user is usually not capable of actuating and releasing the switches in less than one line cycle (16 mSec on a 60 Hz line). The signal is only generated as long as the switch is closed.
A microcomputer 28 in the wall box dimmer 12 is capable of determining the length of time the switch "T" has been actuated and if the switch "T" has been actuated and released a plurality of times in quick succession. The microcomputer is programmed to look for the presence or absence of an AC half cycle signal from the signal detector 32 a fixed period of time after each zero cross of the AC line, preferably 2 mSec. The microcomputer only looks once during each half cycle. The advantage of the signal generator of the prior art is its low cost. The drawback to this type of signal generator is that there are a limited number of signals that can be generated without requiring the user to actuate the same actuator repeatedly or actuate the actuator for an extended period of time in order to perform additional functions. Details of a signal generator according to the prior art are disclosed in issued U.S. Pat. No. 5,248,919, the entire disclosure of which is hereby incorporated by reference. There is a need for a low cost signal generator that does not require the user to actuate the same actuator in different ways to initiate multiple functions.
Also known are phase control lamp dimmers which use a semiconductor device to control the phase of an AC waveform provided to an electric lamp thereby to control the intensity of the lamp. These phase control dimmers are not ordinarily considered to be signal generators of the type contemplated herein. Further, such phase control dimmers, until turned off, produce a phase shaped AC waveform continuously unlike the signal generator described above in connection with FIG. 1.
Other signal generators of the prior art can generate a plurality of control signals, but require a microprocessor in the signal generator which converts the actuator actuations into digital signals for processing by another microprocessor. The drawback to his type of signal generator is the added cost of the microprocessor and its associated lower supply.
Accordingly, there is a need for a low cost signal generator that overcomes the drawbacks of the prior art.